1. Field of the Invention
The present invention is directed to intraocular lenses, and more particularly to accommodating intraocular lenses having more than one focus or an extended depth of focus.
2. Description of the Related Art
A human eye can suffer diseases that impair a patient's vision. For instance, a cataract may increase the opacity of the lens, causing blindness. To restore the patient's vision, the diseased lens may be surgically removed and replaced with an artificial lens, known as an intraocular lens, or IOL. An IOL may also be used for presbyopic lens exchange or other elective ocular surgical procedures.
Monofocal IOLs have a single focal length, or, equivalently, a single power. Unlike the eye's natural lens, which can adjust its focal length within a particular range in a process known as accommodation, these single focal length IOLs cannot accommodate and provide clear vision only over a limited range of distances. As a result, distant objects may appear in focus, while objects at a normal reading distance from the eye may appear blurred.
Vision over a broader range of distances can be obtained either through the use of a multifocal lens, which provides different foci configured to produce focused images for different object distances, or an aspheric lens configured to provide an extended depth of focus or depth of field. While such lenses can improve the overall vision range, there may also be an associated reduction in visual acuity or overall visual quality.
Another approach is to use an accommodating IOL, which can adjust its axial position and/or optical power within a particular range, similar to the eye's natural lens. As a result, the patient can clearly focus on objects in a range of distances from the eye, rather than at a single distance. This ability to accommodate is of tremendous benefit for the patient, and more closely approximates the patient's natural vision than a single focal length IOL. One of the challenges in accommodating IOL's is providing a sufficient range of accommodation with the limited amount of ocular force available from the ciliary muscle. One solution to this problem is to combine an accommodating IOL with a multifocal or extended focus lens. Such approaches are disclosed in U.S. Pat. Nos. 6,503,276, 6,554,859, 6,638,305, and 7,018,409, which are herein incorporated by reference.
Another consideration is the location of the IOL within the eye. In the case of a pseudophakic eye, the IOL that replaces the eye's natural lens is commonly implanted within the capsular bag of the eye. The IOL has an optic, which refracts light that passes through it and forms an image on the retina, and a haptic, which mechanically couples the optic to the capsular bag. In the case of an accommodating IOL, the ciliary muscle and zonules exert a force on the capsular bag, which in turn exerts a force on the optic. The force may be transmitted from the capsular bag directly to the optic, or from the capsular bag through the haptic to the optic.
A desirable optic for an accommodating IOL is one that distorts in response to a squeezing or expanding radial force applied to the optic (i.e., by pushing or pulling on or near the edge of the optic, circumferentially around the optic axis). Under the influence of a squeezing force, the optic bulges slightly in the axial direction, producing more steeply curved anterior and/or posterior faces, and producing an increase in the power of the optic. Likewise, an expanding radial force produces a decrease in the optic power by flattening the optic. This change in power is accomplished in a manner similar to that of the natural eye and is well adapted to accommodation. Furthermore, this method of changing the lens power may reduce undesirable pressures exerted on some of the structures in the eye.
One challenge in implementing such an optic is designing a suitable haptic to couple the optic to the capsular bag. The haptic should allow distortion of the optic in an efficient manner, so that a relatively small ocular force from the ciliary muscle, zonules, and/or capsular bag can produce a relatively large change in power and/or axial location of the image. This may reduce fatigue on the eye, which is generally desirable.
Accordingly, there exists a need for an intraocular lens having a haptic with increased accommodative range and enhanced efficiency in converting a zonular force to a change in power and/or a change in axial location of the image. Better methods of implementing multifocal and extended focal IOL's into accommodating IOL's are also needed as a means for supplementing the overall accommodative range available to the eye.